Almost half of women continue drinking alcohol through pregnancy, and older, wealthier, well-educated women are the worst culprits, new research shows.
The landmark national study of pregnancy also found that 20 per cent of expectant mothers smoke cigarettes daily – many heavily.
Five per cent continue smoking marijuana and two per cent indulge in harder drugs.
The National Drug and Alcohol Research Centre study is the latest to highlight high drinking rates, with 47 per cent of women consuming alcohol during pregnancy and breast-feeding.
While most women drank less than they usually would during this time, lead researcher Cate Wallace said it was clear messages about the dangers of the practice were not getting through.
Tertiary-educated, older, English-speaking women on higher incomes were the most likely to drink, probably because they have entrenched patterns of alcohol consumption, Ms Wallace said.
"Women are having babies later in life when, it seems, it’s harder for them to stop drinking," she said.
The Australian guidelines, which recommend pregnant women consume fewer than seven standard drinks a week and no more than two drinks a day, are currently under review.
"The problem is we know high levels are very harmful but we don’t know how little alcohol is too much, Ms Wallace said.
"It’s safest to stop drinking altogether … but clearly women aren’t doing that."
The study was based on data in the 2004 National Drug Strategy Household Survey and involved about 7,500 women aged 14 to 49, including 1,000 who were pregnant.
It showed that 25 per cent of non-pregnant women smoked cigarettes, and an alarming 20 per cent of pregnant women also smoked.
Almost all of these – 19 per cent – smoked daily, and seven out of ten of them puffed on ten or more cigarettes a day.
"That’s a very high rate, particularly since the links with lower birth weight, premature birth, ectopic pregnancy, spontaneous abortion, still birth, SIDS and asthma are proven," Ms Wallace said.
"We’ve got such great tobacco cessation tools available but we’re not lowering that rate."
Pregnant smokers were a younger demographic than pregnant drinkers, with most aged 25 to 35.
The study, published in the Australian and New Zealand Journal or Public Health, is the first of several research papers investigating health risk to pregnant women.